I am reliably informed by someone who has been digging around this a lot longer than I have that the words "UK only" were also missing from the ANO, not many years ago, on the IMC Rating IFR privileges
Yes, but it is only within the grant of the national authority to allow IFR with a non ICAO rating regardless of the registration, notwithstanding that an FAA IR whilst an ICAO rating departs from the ICAO standard by a long list of differences as do many other IRs.
If DGAC were to tell you they accepted the IMCr for IFR ops then you would be good to go in the same way that if you are a non European national they will recognise your FAA IR in a G reg aircraft.